Semiconductor device and manufacturing method thereof

ABSTRACT

A semiconductor device includes a silicon substrate in which active regions of a memory cell are defined, a gate electrode formed on a device isolation insulating film to extend in a first direction, a first insulating film formed on the silicon substrate and the gate electrode, a first plug formed to penetrate the first insulating film, to overlap with the gate electrode and the first active region, and to extend in a second direction perpendicular to the first direction, a second plug penetrating the first insulating film above the second active region, a second insulating film formed on the first insulating film, and an interconnection buried in the second insulating film, and formed to recede from a side surface of the first plug in the second direction and to cover only part of an upper surface of the first plug.

CROSS-REFERENCE TO RELATED APPLICATION

This application is based upon and claims the benefit of priority of the prior Japanese Patent Application NO. 2009-160837, filed on Jul. 7, 2009, the entire contents of which are incorporated herein by reference.

FIELD

It is related to a semiconductor device and a manufacturing method thereof.

BACKGROUND

There are various types of volatile memories formed on semiconductor substrates. Among them, a SRAM (static random access memory) is able to achieve high-speed operation and is utilized for a cache memory and the like.

A memory cell in the SRAM includes a flip-flop circuit formed of multiple MOS transistors. Information is stored in the flip-flop circuit.

Reduction in the cell size of the SRAM can contribute to downsizing of an electronic device including the SRAM such as a calculator.

Note that 2008 Symposium on VLSI Technology Digest of Technical Papers, p. 106-107, 2008 discloses techniques related to the SRAM.

SUMMARY

According to one aspect discussed herein, there is provided a semiconductor device including a semiconductor substrate in which a first active region and a second active region of a memory cell of a static random access memory are defined by a device isolation insulating film, a gate electrode formed over the device isolation insulating film and the first active region, and extending in a first direction, a first insulating film formed over the semiconductor substrate and the gate electrode, a first plug formed to penetrate the first insulating film, to overlap with the gate electrode and the first active region, and to have a rectangular planar shape extending in a second direction perpendicular to the first direction, a second plug formed to penetrate the first insulating film over the second active region, a second insulating film formed over the first insulating film, and a interconnection buried in the second insulating film, and formed to extend from a position over the first c plug to a position over the second plug while receding from a side surface of the plug in the second direction, and to cover only a part of an upper surface of the first plug.

According to another aspect discussed herein, there is provided a semiconductor device including a semiconductor substrate in which a first active region and a second active region are defined by a device isolation insulating film, a gate electrode formed over the device isolation insulating film and the first active region and extending in a first direction, a first insulating film formed over the semiconductor substrate and the gate electrode, a first plug formed to penetrate the first insulating film, to overlap with the gate electrode and the first active region, and to have a rectangular planar shape extending in a second direction perpendicular to the first direction, a second insulating film formed over the first insulating film, a second plug formed to penetrate the first insulating film and the second insulating film over the second active region, a interconnection formed in the second insulating film, formed integrally with the first plug and the second plug, and extending from a position over the first plug to a position over the second copper-containing plug, and a third plug formed to penetrate the first insulating film and the second insulating film.

According to yet another aspect discussed herein, there is disclosed a method of manufacturing a semiconductor device including defining, in a semiconductor substrate, a first active region and a second active region of a memory cell of a static random access memory by forming a device isolation insulating film over the semiconductor substrate, forming a gate electrode, extending in a first direction, over the device isolation insulating film and the first active region, forming a first insulating film over the semiconductor substrate and the gate electrode, forming a first hole in the first insulating film, the first hole overlapping with the gate electrode and the first active region and having a rectangular planar shape extending in a second direction perpendicular to the first direction, forming a second hole in the first insulating film over the second active region, forming a first plug and a second plug respectively in the first hole and the second hole, forming a second insulating film over the first plug, the second plug, and the first insulating film, forming a trench in the second insulating film, the trench extending from a position over the first plug to a position over the second plug, the trench being formed at a distance from a side surface of the first plug in the second direction, and forming a interconnection in the trench.

According to still another aspect discussed herein, there is provided a method of manufacturing a semiconductor device including defining, in a semiconductor substrate, a first active region and a second active region of a memory cell of a static random access memory by forming a device isolation insulating film over the semiconductor substrate, forming a gate electrode, extending in a first direction, over the device isolation insulating film and the first active region, forming a first insulating film over the semiconductor substrate and the gate electrode, forming a second insulating film over the first insulating film, forming a first hole, a second hole and a third hole by patterning the first insulating film and the second insulating film, the first hole having a rectangular planar shape overlapping with the gate electrode and the first active region and extending in a second direction perpendicular to the first direction, the second hole being located over the second active region, forming a trench by patterning the second insulating film, the trench extending from a position over the first hole to a position over the second hole, and forming first, second, and third plugs in the first, second, and third holes and forming an interconnection in the trench, thereby forming the interconnection integrally formed with the first plug and the second plug.

Other objects and further features of the present application will become apparent from the following detailed description when read in conjunction with the attached drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an enlarged plan view illustrating an example of a planar layout of a SRAM memory cell;

FIG. 2 is an equivalent circuit diagram of the SRAM memory cell;

FIG. 3 is a cross-sectional view taken along an I-I line in FIG. 1;

FIG. 4 is a graph illustrating a relation between a gate length of a MOS transistor and resistance of a tungsten plug having a diameter suitable for the gate length;

FIGS. 5A to 5J are cross-sectional views during manufacture of a semiconductor device according to a first embodiment;

FIGS. 6A to 6F are plan views during manufacture of the semiconductor device according to the first embodiment;

FIGS. 7A to 7F are cross-sectional views during manufacture of a semiconductor device according to a second embodiment;

FIGS. 8A to 8D are plan views during manufacture of the semiconductor device according to the second embodiment;

FIGS. 9A to 9C are cross-sectional views during manufacture of a semiconductor device according to a comparative example; and

FIGS. 10A to 10F are cross-sectional views during manufacture of a semiconductor device according to a third embodiment.

DESCRIPTION OF EMBODIMENTS

Prior to explaining the present embodiments, preliminary matter will be explained.

The inventor has conducted various studies on planar layouts of memory cells in order to achieve reduction in the cell size of a SRAM.

FIG. 1 illustrates one of such planar layouts which is an enlarged plan view of a memory cell C in the SRAM. In FIG. 1, a word-line direction is indicated by X while a bit-line direction is indicated by Y.

In this example, a device isolation insulating film 2 for STI (shallow trench isolation) is formed on a silicon substrate 1 and first active regions 1 a and second active regions lb of the silicon substrate 1 are defined by this device isolation insulating film 2.

Moreover, gate electrodes 5 made of polycrystalline silicon are formed on these active regions 1 a and 1 b and on the device isolation insulating film 2 so as to extend in the word-line direction.

Two driver transistors TR_(drive), two access transistors TR_(access), and two load transistors TR_(load) are formed in a memory cell C at portions where the gate electrodes 5 overlap with the active regions 1 a and 1 b, as illustrated in FIG. 1.

Further, first to third tungsten plugs 15 a to 15 c for drawing source-drain regions of the above-described transistors TR_(drive), TR_(access), and TR_(load) to an upper layer are formed on the active regions 1 a and 1 b.

Among these tungsten plugs, the first tungsten plug 15 a has a rectangular planar shape overlapping with the gate electrode 5 and the first active region 1 a, and has a function to connect the gate electrode 5 directly to the first active region 1 a. This plug is also referred to as a shared contact.

Meanwhile, a first copper-containing interconnection 18 a having an L-shaped planar shape is formed on this first tungsten plug 15 a. The first copper-containing interconnection 18 a extends in the bit-line direction Y and plays a role in connecting the first tungsten plug 15 a to the second tungsten plug 15 b.

Moreover, the first copper-containing interconnection 18 a is formed to cover the entire upper surface of the first tungsten plug 15 a in order to reduce contact resistance with the first tungsten plug 15 a.

In the meantime, a copper-containing pad 18 b having a rectangular planar shape extending in the word-line direction X is formed on the third tungsten plug 15 c.

FIG. 2 is an equivalent circuit diagram of the memory cell C of this SRAM.

As illustrated in FIG. 2, in one memory cell C, the respective gate electrodes 5 of the two access transistors TR_(access) are electrically connected to word lines WL. Meanwhile, a bit line BL is electrically connected to the respective source-drain regions of the two access transistors TR_(access).

FIG. 3 is a cross-sectional view taken along an I-I line in FIG. 1.

As illustrated in FIG. 3, the gate electrodes 5 are formed on the silicon substrate 1 with gate insulating films 4, each made of a thermal oxide film, interposed therebetween.

Meanwhile, p-type source-drain regions 7 are formed in the silicon substrate 1 beside the gate electrodes 5, and resistance in surface layer portions of the source-drain regions 7 is reduced by refractory metal silicide layers 10 such as nickel silicide layers.

Then, a cover insulating film 11 made of silicon nitride and a first insulating film 12 made of silicon oxide are formed in this order on the gate electrodes 5, and the first tungsten plug 15 a and the second tungsten plug 15 b described above are buried in these insulating films 11 and 12.

Moreover, a first copper diffusion prevention insulating film 13 made of silicon carbide (SiC) and a second insulating film 14 made of silicon oxide are formed in this order on the first insulating film 12.

A first trench 14 a and a second trench 14 b are formed in these insulating films 13 and 14, and the first copper-containing interconnection 18 a and the copper-containing pad 18 b described above are buried in these trenches by a single damascene method. As described previously, the first copper-containing interconnection 18 a is formed to cover the entire upper surface of the first tungsten plug 15 a in order to reduce the contact resistance with the first tungsten plug 15 a.

Further, a second copper diffusion prevention insulating film 21 made of silicon carbide and a third insulating film 22 made of silicon oxide are formed on the first copper-containing interconnection 18 a, the copper-containing pad 18 b, and the second insulating film 14.

A second copper-containing interconnection 25 and a copper-containing plug 24 are buried in the third insulating film 22. Here, the copper-containing plug 24 is electrically connected to the second copper-containing plug 15 b via the copper-containing pad 18 b.

By connecting the vertically located plugs 15 b and 24 to each other via the copper-containing pad 18 b as described above, it is possible to ensure the contact areas between the copper-containing pad 18 b and the respective plugs 15 b and 24, and thereby to prevent an increase in the contact resistance between these plugs 15 b and 24.

Moreover, the area of the copper-containing pad 18 b is increased by forming the planar shape of the copper-containing pad 18 b into the rectangle that extends in the word-line direction as illustrated in FIG. 1. Therefore, when forming the second trench 14 b by photolithography for burying therein the copper-containing pad 18 b, the shape of the trench 14 b is less affected by an optical proximity effect. In this way, it is possible to suppress deformation of the shape of the copper-containing pad 18 b and thereby to achieve the above-described effect of preventing the increase in the contact resistance between the respective plugs 15 b and 24.

However, according to the planar layout of the SRAM illustrated in FIG. 1, the first copper-containing interconnection 18 a is formed into the L-shaped planar shape in order to cover the entire upper surface of the first tungsten plug 15 a. As a consequence, a distance D between the first copper-containing interconnection 18 a and the copper-containing pad 18 b is reduced.

Therefore, it is necessary to separate the first copper-containing interconnection 18 a from the copper-containing pad 18 b along the bit-line direction Y in order to reduce a risk of an electrical short circuit between the first copper-containing interconnection 18 a and the copper-containing pad 18 b attributable to the shorter distance D. Accordingly, this structure has a problem that it is not possible to achieve reduction in the area of the memory cell C because the memory cell C is extended in the bit-line direction Y.

Further, the first copper-containing interconnection 18 a having the L-shape has the more complicated contour as compared to a straight interconnection. Accordingly, OPC (optical proximity correction) processing to be performed on an exposure mask used for forming the first trench 14 a in the lithography is also complicated. For this reason, there is another problem that it takes a long time for designing the SRAM due to time-consuming calculation for the OPC.

On the other hand, as the generation of the MOS transistors advances and gate lengths thereof are shortened, the diameters of the tungsten plugs also need to be formed smaller so as to achieve reduction in size of the MOS transistors. However, the smaller diameters of the tungsten plugs may increase the resistance of tungsten plugs and may adversely affect characteristics of the MOS transistors.

FIG. 4 is a graph illustrating a relation between a gate length of a MOS transistor and resistance of a tungsten plug having a diameter suitable for the gate length.

Note that FIG. 4 also illustrates a relation between the gate length and resistance of a copper-containing plug having a diameter suitable for the gate length for the purpose of comparison. Moreover, on resistance of the MOS transistor is also illustrated in FIG. 4. Here, the on resistance is resistance between a source and drain when the gate of the MOS transistor is in an on state. FIG. 4 illustrates the on resistance in three types of channel widths, namely, wide, middle, and narrow widths in order to indicate how much the on resistance varies depending on the size of the channel width.

It is deemed desirable to set the resistance of the plug equal to or below about 1/10 as large as the on resistance in order to operate the MOS transistor normally.

As illustrated in FIG. 4, the resistance of the tungsten plug exceeds 1/10 of the on resistance in a generation where the gate length is shorter than 45 nm. Hence, it is understood that the tungsten plugs are unsuitable in this generation or later.

On the other hand, the resistance of the copper-containing plug exhibits a value equal to or below 1/10 of the on resistance even in the generation where the gate length is shorter than 45 nm.

Accordingly, in the above-described SRAM using the first to third tungsten plugs 15 a to 15 c, it is not possible to reduce the gate lengths of the transistors TR_(drive), TR_(access), and TR_(load) without affecting the characteristics of these transistors.

In view of this knowledge, the inventor has achieved embodiments as described below.

First Embodiment

FIGS. 5A to 5J are cross-sectional views during manufacture of a semiconductor device according to this embodiment and FIGS. 6A to 6F are plan views thereof.

Note that both of a first cross section taken along the word-line direction and a second cross section taken along the bit-line direction are illustrated throughout FIGS. 5A to 5J. The same applies to respective cross-sectional views illustrated in conjunction with a second embodiment and a third embodiment to be described later.

This semiconductor device is a SRAM, which is manufactured as described below.

First, as illustrated in FIG. 5A, a device isolation trench 31 x having a depth of about 300 nm is formed on a silicon substrate 31 serving as a semiconductor substrate.

Then, after a silicon oxide film serving as a device isolation insulating film 32 for the STI is formed on the entire upper surface of the silicon substrate 31 by a CVD (chemical vapor deposition) method, an excessive portion of the device isolation insulating film 32 on the surface of the silicon substrate 31 is polished and removed by a CMP (chemical mechanical polishing) method, thereby leaving the device isolation insulating film 32 only in the device isolation trench 31 x.

Thereafter, the device isolation insulating film 32 is subjected to annealing under conditions of a substrate temperature of about 1000° C. and processing time of about 30 seconds in order to increase a film density of the device isolation insulating film 32.

FIG. 6A is the plan view after completion of the above-described steps. Here, the second cross section in FIG. 5A corresponds to a cross section taken along an X1-X1 line in FIG. 6A and the first cross section in FIG. 5A corresponds to a cross section taken along a Y1-Y1 line in FIG. 6A.

Moreover, the word-line direction is indicated by X while the bit-line direction perpendicular thereto is indicated by Y in FIG. 6A.

As illustrated in FIG. 6A, first active regions 31 a and second active regions 31 b are defined in the silicon substrate 31 by the device isolation insulating film 32. All of these active regions 31 a and 31 b extend in the bit-line direction Y.

Next, steps to be carried out in order to obtain a cross-sectional structure illustrated in FIG. 5B will be described.

First, phosphorus is ion-implanted into the silicon substrate 31 in the first active region 31 a under conditions of acceleration energy of 300 keV and a dose amount of 3×10¹³ cm⁻², thereby forming an n-well 33.

Further, an n-type impurity diffused region for threshold adjustment is formed at a surface layer portion of the n-well 33 by ion implantation. As for the n-type impurity, arsenic is ion-implanted under conditions of acceleration energy of 100 keV and a dose amount of 4×10¹² cm⁻², for example.

In the meantime, a p-well 39 and a p-type impurity diffused region for threshold adjustment are formed in the second active region 31 b. In order to form the p-well 39, boron is ion-implanted under conditions of acceleration energy of 150 keV and a dose amount of 3×10¹³ cm⁻², for example. Meanwhile, as for the p-type impurity for threshold adjustment, boron is ion-implanted under conditions of acceleration energy of 10 keV and a dose amount of 4×10¹² cm⁻², for example.

Subsequently, an annealing process is performed under conditions of a substrate temperature of 1000° C. and processing time of 10 seconds for the purpose of diffusing the impurities in the respective wells 33 and 39. Such an annealing process is also referred to as well annealing.

Then, a thermal oxide film having a thickness of about 1.2 nm is formed as a gate insulating film 34 by thermally oxidizing the surface of the silicon substrate 31. Although conditions of the thermal oxidation are not particularly limited, the gate insulating film 34 of this embodiment is formed by a RTO (rapid thermal oxidation) method under a condition of a substrate temperature of about 900° C.

Moreover, a polycrystalline silicon film having a film thickness of about 100 nm is formed on the gate insulating film 34 by a CVD method, and a gate electrode 35 is formed by patterning the polycrystalline silicon film.

Thereafter, boron serving as a p-type impurity is ion-implanted into the silicon substrate while using the gate electrode 35 as a mask, thereby forming a p-type source-drain extension 36 a in the silicon substrate 31 in the first active region 31 a. Conditions for the ion implantation include acceleration energy of 0.5 keV and a dose amount of 1×10¹⁵ cm⁻², for example.

In the meantime, arsenic is ion-implanted into the silicon substrate 31 in the second active region 31 b under conditions of acceleration energy of 3 keV and a dose amount of 1×10¹⁵ cm⁻², thereby forming an n-type source-drain extension 36 b.

Then, after forming an insulative side wall made of a silicon oxide film beside the respective gate electrodes 35, a p-type source-drain region 37 a is formed by ion-implanting a p-type impurity into the silicon substrate 31 in the first active region 31 a. As for the p-type impurity, boron is ion-implanted under conditions of acceleration energy of 5 keV and a dose amount of 2×10¹⁵ cm⁻².

In the meantime, phosphorus serving as an n-type impurity is ion-implanted into the silicon substrate 31 in the second active region 31 b under conditions of acceleration energy of 15 keV and a dose amount of 2×10¹⁵ cm⁻², thereby forming an n-type source-drain region 37 b.

Thereafter, a stacked film including a nickel film and a titanium nitride film is formed on the entire upper surface of the silicon substrate 31 by a sputtering method, and then a refractory metal silicide layer 40 such as a nickel silicide layer is formed by annealing the stacked film to be reacted with the silicon. Although conditions for the annealing are not particularly limited, the substrate temperature is set in a range from 400° C. to 550° C. while the processing time is set in a range from several seconds to several tens of minutes in this embodiment. Meanwhile, the thickness of the nickel film is set in a range from 5 nm to 20 nm, for example.

After the annealing process, the unreacted nickel film on the device isolation insulating film 32 is removed by a wet etching method using a mixed solution of sulfuric acid and hydrogen peroxide water as an etchant. As a result, the refractory metal silicide layer 40 is left only on the source-drain regions 37 a and 37 b and on the gate electrodes 35.

FIG. 6B is the plan view after completion of the above-described steps. Here, the second cross section in FIG. 5B corresponds to a cross section taken along an X2-X2 line in FIG. 6B and the first cross section in FIG. 5B corresponds to a cross section taken along a Y2-Y2 line in FIG. 6B.

As illustrated in FIG. 6B, the gate electrodes 35 are formed respectively on the device isolation insulating film 32 and on the active regions 31 a and 31 b.

Moreover, two driver transistors TR_(drive), two access transistors TR_(access), and two load transistors TR_(load) are formed in a memory cell C as illustrated in FIG. 6B at portions where the gate electrodes 35 overlap with the respective active regions 31 a and 31 b.

Meanwhile, the access transistors TR_(access) and the driver transistors TR_(drive) share the respective source-drain region in the second active regions 31 b.

An equivalent circuit of the memory cell including these transistors TR_(drive), TR_(access), and TR_(load) is similar to FIG. 2 illustrated in conjunction with the preliminary matter.

Subsequently, as illustrated in FIG. 5C, a silicon nitride film serving as a cover insulating film 41 is formed in a thickness of about 50 nm on the entire upper surface of the silicon substrate 31 by the CVD method.

Moreover, a silicon nitride film is formed in a thickness of about 500 nm on the cover insulating film 41 by a thermal CVD method. The silicon oxide film thus formed is used as a first insulating film 42.

Subsequently, as illustrated in FIG. 5D, a photoresist is coated on the first insulating film 42, and a first resist pattern 46 provided with hole-shaped windows 46 a to 46 c is formed by exposing and developing the photoresist.

Then, the cover insulating film 41 and the first insulating film 42 are dry etched using the first resist pattern 46 as a mask, thereby forming first to third holes 42 a to 42 c on these insulating films.

The dry etching is performed by RIE (reactive ion etching) to change etching gases between an etching process on the first insulating film 42 and an etching process on the cover insulating film 41. In the etching process on the first insulating film 42, mixed gas of C₂F₆ gas and CH₃ gas is used as an etching gas while the cover insulating film 41 serves as an etching stopper. Meanwhile, in the etching process on the cover insulating film 41, CF₄ gas is used as an etching gas while the refractory metal silicide layer 40 serves as an etching stopper.

As illustrated in the first cross section, both of the first hole 42 a and the third hole 42 c are formed on the p-type source-drain region 37 a, and the first hole 42 a is formed to further overlap with the gate electrode 35.

Meanwhile, as illustrated in the second cross section, the second hole 42 b is formed on the n-type source-drain region 37 b.

Thereafter, the first resist pattern 46 is removed.

Next, steps to be carried out in order to obtain a cross-sectional structure illustrated in FIG. 5E will be described.

First, a tantalum film and a tantalum nitride film are formed in this order as a barrier metal film in the respective holes 42 a to 42 c and on an upper surface of the first insulating film 42 by the sputtering method. As for film thicknesses of the respective films, the tantalum film is set to about 5 nm while the tantalum nitride film is set to about 10 nm.

Then, a copper film is formed as a seed layer on this barrier metal film by the sputtering method and a copper plated film is formed using the seed layer as a power feeding layer, thereby completely burying the respective holes 42 a to 42 c with the copper plated film.

Thereafter, the excessive copper plated film, the seed layer, and the barrier metal film on the first insulating film 42 are polished and removed by the CMP method. In this way, first to third copper-containing plugs 45 a to 45 c penetrating the first insulating film 42 are formed inside the respective holes 42 a to 42 c.

FIG. 6C is the plan view after completion of the above-described steps. Here, the second cross section in FIG. 5E corresponds to a cross section taken along an X3-X3 line in FIG. 6C and the first cross section in FIG. 5E corresponds to a cross section taken along a Y3-Y3 line in FIG. 6C.

In FIG. 6C, illustration of the cover insulating film 41 and the first insulating film 42 is omitted for the purpose of preventing complication of the drawing.

As illustrated in FIG. 6C, the first copper-containing plug 45 a is formed to overlap with the gate electrode 35 and the first active region 31 a, and is formed into a rectangular planar shape so as to correspond to the first hole 42 a (see FIG. 5E). The extending direction of the first copper-containing plug 45 a is parallel to the bit-line direction Y.

Meanwhile, each of the second copper-containing plug 45 b and the third copper-containing plug 45 c is formed into a square planar shape.

Next, steps to be carried out in order to obtain a cross-sectional structure illustrated in FIG. 5F will be described.

First, a silicon carbide film serving as a first copper diffusion prevention insulating film 43 is formed in a thickness of about 50 nm on the first insulating film 42 and on the first to third copper-containing plugs 45 a to 45 c by the CVD method.

Further, a silicon oxycarbide (SiOC) film is formed in a thickness of about 150 nm on the first copper diffusion prevention insulating film 43 by the CVD method, and the silicon oxycarbide film thus formed is used as a second insulating film 44.

Then, after forming a second resist patter on the second insulating film 44, the first copper diffusion prevention insulating film 43 and the second insulating film 44 are dry etched using the second resist pattern 47 as a mask, thereby forming a first trench 44 a and a second trench 44 b in these insulating films.

The dry etching is performed by the RIE. In the RIE, etching gas containing either CHF-based gas or CF-based gas is used as etching gas for the second insulating film 44. Here, it is also possible to add inert gas such as argon gas or nitrogen gas to the etching gas.

Meanwhile, gas containing either SO₂ gas or NF₃ gas is used as etching gas for the first copper diffusion prevention insulating film 43. Since the first insulating film 42 functions as the etching stopper against this etching gas, the first insulating film 42 is prevented from being etched when forming the trenches 44 a and 44 b.

As illustrated in the second cross section, the first trench 44 a thus formed extends from a position over the first copper-containing plug 45 a to a position over the second copper-containing plug 45 b. Meanwhile, as illustrated in the first cross section, the first trench 44 a is formed away in the bit-line direction Y from a side surface 45 x out of side surfaces of the first copper-containing plug 45 a, which is located close to the gate electrode 35.

In the meantime, the second trench 44 b is formed over the third copper-containing plug 45 c and in the respective films 43 and 44 therearound.

Thereafter, the second resist pattern 47 is removed.

Next, steps to be carried out in order to obtain a cross-sectional structure illustrated in FIG. 5G will be described.

First, a tantalum film in a thickness of about 5 nm and a tantalum nitride film in a thickness of about 10 nm are formed in this order as a barrier metal film in the respective trenches 44 a and 44 b and on an upper surface of the second insulating film 44 by the sputtering method.

Further, a copper film is formed as a seed layer on this barrier metal film by the sputtering method and a copper plated film is formed by an electrolytic plating method while applying electricity to the seed layer, thereby completely burying the respective trenches 44 a and 44 b with the copper plated film.

Thereafter, the excessive copper plated film, the seed layer, and the barrier metal film on the second insulating film 44 are polished and removed by the CMP method. In this way, a first copper-containing interconnection 48 a is formed in the first trench 44 a and a copper-containing pad 48 b is formed in the second trench 44 b. The above-described method of forming the first copper-containing interconnection 48 a and the copper-containing pad 48 b in the process different from the process to form the respective copper-containing plugs 45 a to 45 c is referred to as a single damascene method.

Here, since the first trench 44 a is formed away from the side surface 45 x of the first copper-containing plug 45 a, the first copper-containing interconnection 48 a is formed to cover only a part of an upper surface of the first copper-containing plug 45 a.

Meanwhile, the copper-containing pad 48 b is formed on the third copper-containing plug 45 c in a manner that the pad 48 b is buried in the second insulating film 44 around the plug 45 c.

FIG. 6D is the plan view after completion of the above-described steps. Here, the second cross section in FIG. 5G corresponds to a cross section taken along an X4-X4 line in FIG. 6D and the first cross section in FIG. 5G corresponds to a cross section taken along a Y4-Y4 line in FIG. 6D.

As illustrated in FIG. 6D, the first copper-containing interconnection 48 a extends from the position over the first copper-containing plug 45 a to the position over the second copper-containing plug 45 b, and has a rectangular planar shape extending in the word-line direction X.

Further, the first copper-containing interconnection 48 a is formed to recede from the side surface 45 x of the first copper-containing plug 45 a in a recession amount ΔY in the bit-line direction Y, and thereby covers only a part of the upper surface of the first copper-containing plug 45 a.

Here, the planar shape of the first copper-containing interconnection 48 a is not limited only to the above-mentioned rectangular shape as long as the first copper-containing interconnection 48 a recedes from the side surface 45 x and to expose the upper surface of the first copper-containing plug 45 a as described previously. For example, the first copper-containing interconnection 48 a may also be formed into an L-shape as similar to the first copper-containing interconnection 18 a (see FIG. 1) of the preliminary matter.

Meanwhile, the planar shape of the copper-containing pad 48 b is a rectangular shape extending in the word-line direction X. By applying this shape, the shape of the trench 44 b (see FIG. 5F) is less affected by an optical proximity effect when forming the second trench 44 b by photolithography for burying therein the copper-containing pad 48 b as similar to the preliminary matter. Hence it is possible to suppress deformation of the shape of the copper-containing pad 48 b.

Subsequently, as illustrated in FIG. 5H, a second copper diffusion prevention insulating film 51 and a third insulating film 52 are formed in this order respectively on the second insulating film 44, the first copper-containing interconnection 48 a, and the copper-containing pad 48 b by the CVD method.

Of these insulating films, a silicon carbide film having a thickness of about 50 nm is formed as the second copper diffusion prevention insulating film 51 and a silicon oxycarbide film having a thickness of about 250 nm is formed as the third insulating film 52.

Thereafter, a third resist pattern 53 provided with a hole-shaped window 53 a is formed on the third insulating film 52, and a fourth hole 52 a is formed in the copper-containing pad 48 b by dry etching the respective insulating films 51 and 52 using the third resist pattern 53 as a mask.

The dry etching is performed by the RIE. Either CHF-based gas or CF-based gas is used as etching gas for the third insulating film 52. It is also possible to add inert gas such as argon gas or nitrogen gas to the etching gas.

Meanwhile, gas containing either SO₂ gas or NF₃ gas is used as etching gas for the second copper diffusion prevention insulating film 51.

Thereafter, the third resist pattern 53 is removed.

Subsequently, as illustrated in FIG. 5I, a photoresist is coated on the third insulating film and in the fourth hole 52 a, and a fourth resist pattern 54 provided with a window 54 a having a wiring trench shape is formed by exposing and developing the photoresist. The fourth resist pattern 54 in the bottom portion of the fourth hole 52 a is not removed by development, but is left in the hole 52 a.

Then, the third insulating film 52 is dry etched to a halfway depth by the RIE using the fourth resist pattern 54 as a mask. In this way, a third trench 52 b exposing the fourth hole 52 a at a bottom and a fourth trench 52 c located at a distance from the third trench 52 b are formed on the third insulating film 52.

The etching gas containing either CHF-based gas or CF-based gas, or these gas with addition of inert gas such as argon gas or nitrogen gas is used for etching gas in this process.

Thereafter, the fourth resist pattern 54 is removed.

Next, steps to be carried out in order to obtain a cross-sectional structure illustrated in FIG. 5J will be described.

First, a tantalum film in a thickness of about 5 nm and a tantalum nitride film in a thickness of about 10 nm are formed in this order as a barrier metal film in the respective trenches 52 b and 53 c and the fourth hole 52 a, and on an upper surface of the third insulating film 52 by the sputtering method.

Further, a copper film is formed as a seed layer on this barrier metal film by the sputtering method and a copper plated film is formed by the electrolytic plating method while applying electricity to the seed layer, thereby completely burying the respective trenches 52 b and 52 c as well as the fourth hole 52 a with the copper plated film.

Thereafter, the excessive copper plated film, the seed layer, and the barrier metal film on the third insulating film 52 are polished and removed by the CMP method. In this way, a fourth copper-containing plug 55 a penetrating the third insulating film 52 and a second copper-containing interconnection 55 b are integrally formed in the third trench 52 b and the fourth hole 52 a, respectively.

Meanwhile, a third copper-containing interconnection 55 c constituting a word line (WL) is formed in the fourth trench 52 c.

The above-described method of integrally forming the fourth copper-containing interconnection 55 a and the second copper-containing pad 55 b is referred to as a dual damascene method.

The fourth copper-containing plug 55 a is electrically connected to the third copper-containing plug 45 c via the copper-containing pad 48 b. Here, contact areas between the copper-containing pad 48 b and the respective plugs 45 c and 55 a are ensured by connecting the respective plugs 45 c and 55 a to each other via the copper-containing pad 48 b. Accordingly, it is possible to prevent an increase in the contact resistance between these plugs 45 c and 55 a as compared to the case of connecting the respective plugs 45 c and 55 a directly to each other without the copper-containing pad 48 b interposed therebetween.

Thereafter, a silicon carbide film serving as a third copper diffusion prevention insulating film 57 is formed in a thickness of about 50 nm on respective upper surfaces of the third insulating film 52 and the copper-containing interconnections 55 b and 55 c by the CVD method.

FIG. 6E is the plan view after completion of the above-described steps. Here, the second cross section in FIG. 5J corresponds to a cross section taken along an X5-X5 line in FIG. 6E and the first cross section in FIG. 5J corresponds to a cross section taken along a Y5-Y5 line in FIG. 6E.

Thereafter, as illustrated in FIG. 6F, a bit line BL and a fourth copper-containing interconnection 56 are formed over the third copper-containing interconnection 55 c by the dual damascene method.

In this way, a basic structure of the semiconductor device according to this embodiment is finished.

According to the above-described embodiment, as illustrated in the plan view of FIG. 6D, the first copper-containing interconnection 48 a is formed to recede from the side surface 45 x of the first copper-containing plug 45 a in the bit-line direction Y to thereby cover only a part of the upper surface of the first copper-containing plug 45 a with the first copper-containing interconnection 48 a.

In this way, it is possible to provide a margin for the distance D between the first copper-containing interconnection 48 a and the conductor pattern located in the same layer as the first copper-containing interconnection 48 a, such as the copper-containing pad 48 b, as compared to the case of forming the first copper-containing interconnection 48 a into the L-shape as in the preliminary matter. Therefore, it is possible to downsize the memory cell C by reducing the distance D.

The inventor performed calculations in terms of the generation having the gate length of 22 nm, for example. In the example of the preliminary matter illustrated in FIG. 1, the length of the memory cell C in the word-line direction X is 0.5 μm while the length thereof in the bit-line direction Y is 0.264 μm. Hence the area of the memory cell C is 0.13 μm².

On the other hand, in the layout of this embodiment illustrated in FIG. 6D, the length of the memory cell C in the word-line direction X is 0.562 μm while the length thereof in the bit-line direction Y is 0.184 μm. Hence, the area of the memory cell C is 0.10 μm². Here, the reason why the length in the word-line direction X of the memory cell C of the embodiment is longer than the length in the preliminary matter is that a length A in the word-line direction X of another copper-containing pad 48 c is increased in order to ensure to the area of the copper-containing pad 48 c which is formed on the same layer as the copper-containing pad 48 b. Another reason is that a clearance B is intended to be ensured between the copper-containing pad 48 c and still another copper-containing pad 48 d.

In this manner, according to this embodiment, it is possible to reduce the area of the memory cell C by about 23% less than the relevant area in the case of the preliminary matter. Thus it is possible to confirm that the embodiment can contribute to reduction in the cell size of the SRAM.

Moreover, by forming the first copper-containing interconnection 48 a receding from the side surface 45 x of the first copper-containing plug 45 a in the bit-line direction, the planar shape of the first copper-containing interconnection 48 a is formed into the simple rectangular shape extending in the word-line direction.

In this way, it is possible to simplify the OPC processing to be performed on an exposure mask when exposing the second resist pattern 47 (see FIG. 5F) as compared to the case of forming the first copper-containing interconnection 48 a into the L-shape as in the preliminary matter. Hence it is possible to design the exposure mask in a shorter period of time.

Furthermore, in this embodiment, the copper-containing plugs having lower resistance than that of the tungsten plugs are formed as the respective plugs 45 a to 45 c to be connected to the respective active regions 31 a and 31 b. Accordingly, as illustrated in FIG. 4, the resistance of the respective copper-contain plugs 45 a to 45 c can be maintained at about 1/10 or less of the on resistance of the MOS transistor, even when the MOS transistor comes to have a gate length of 45 nm or below with the progress of generations. In this way, it is possible to downsize the respective transistors TR_(drive), TR_(access), and TR_(load) while retaining the characteristics of these transistors, and thereby to further downsize the memory cell of the SRAM.

Meanwhile, since the first copper-containing plug 45 a has smaller resistance as compared to the tungsten plug, it is possible to maintain the contact resistance between the first copper-containing plug 45 a and the copper-containing interconnection 48 a even when only a part of the upper surface of the first copper-containing plug 45 a is covered with the copper-containing interconnection 48 a.

Second Embodiment

FIGS. 7A to 7F are cross-sectional views during manufacture of a semiconductor device according to this embodiment, and FIGS. 8A to 8D are plan views thereof. In FIGS. 7A to 7F, the same constituents as those in the first embodiment are designated by the same reference numerals as the first embodiment, and description thereof will be omitted in the following.

In the first embodiment, the first copper-containing interconnection 48 a is formed by the single damascene method as described with reference to FIG. 5G. In contrast, in this embodiment, the corresponding copper-containing interconnection is formed by the dual damascene method.

To manufacture the semiconductor device according to this embodiment, the steps in the first embodiment as illustrated in FIGS. 5A to 5C are firstly executed, and then a silicon carbide film serving as an etching stopper film 60 is formed in a thickness of about 50 nm on the first insulating film 42 by the CVD method as illustrated in FIG. 7A.

Here, the etching stopper film 60 is not limited only to the silicon carbide film. It is also possible to form a silicon nitride film as the etching stopper film 60 instead.

Moreover, a second insulating film 61 and an antireflection insulating film 62 are formed in this order on this etching stopper film 60. The second insulating film 61 is a silicon oxide film in a thickness of about 150 nm which is formed by the CVD method, for example. Meanwhile, as for the antireflection insulating film 62, a silicon nitride film is formed in a thickness of about 30 nm by the CVD method.

FIG. 8A is the plan view after completion of the above-described steps. Here, the second cross section in FIG. 7A corresponds to a cross section taken along an X6-X6 line in FIG. 8A and the first cross section in FIG. 7A corresponds to a cross section taken along a Y6-Y6 line in FIG. 8A.

Here, the respective insulating films 41, 42, and 60 to 62 are omitted in FIG. 8A in order to facilitate the understanding of planar layouts of the first and second active regions 31 a and 31 b as well as the gate electrodes 35.

As illustrated in FIG. 8A, the driver transistors TR_(drive), the access transistors TR_(access), and the load transistors TR_(load) are formed as similar to the first embodiment at the portions where the gate electrodes 35 overlap with the respective active regions 31 a and 31 b.

Subsequently, as illustrated in FIG. 7B, a first resist pattern 63 provided with hole-shaped windows 63 a to 63 c is formed on the antireflection insulating film 62.

The first resist pattern 63 is used as a mask for etching the respective insulating films 42 and 60 to 62. The first to third holes 42 a to 42 c are formed in these insulating films 42 and 60 to 62 by the RIE.

The etching gas used in the RIE is not particularly limited. For example, gas containing SO₂ gas or NF₃ gas is used as the etching gas for the etching stopper film 60.

Meanwhile, the mixed gas of C₂F₆ gas and CH₃ gas is used as the etching gas for the first insulating film 42 and the second insulating film 61, for example. When using this etching gas, the etching rate of the cover insulating film 41 is lower than that of the first insulating film 42. Accordingly, this etching process stops on the upper surface of the cover insulating film 41.

As illustrated in the first cross section, among the respective holes thus formed, both of the first hole 42 a and the third hole 42 c are formed on the p-type source-drain region 37 a and the first hole 42 a is formed to further overlap with the gate electrode 35.

Meanwhile, as illustrated in the second cross section, the second hole 42 b is formed on the n-type source-drain region 37 b.

Subsequently, as illustrated in FIG. 7C, the cover insulating film 41 below the respective contact holes 42 a to 42 c is dry etched and removed by performing the RIE while changing the etching gas into the CF₄ gas.

Thereafter, the first resist pattern 63 is removed.

Next, as illustrated in FIG. 7D, a photoresist is coated again on the antireflection insulating film 62, and then is developed by exposure to form a second resist pattern 65 provided with a window 65 a having a wiring trench shape and overlapping with the first hole 42 a.

The second resist pattern 65 in the bottom portions of the first hole 42 a and the second hole 42 b is not removed by development but is left in these holes 42 a and 42 b. Meanwhile, the third hole 42 c is completely filled with the second resist pattern 65.

Then, the antireflection insulating film 62 and the second insulating film 61 are dry etched by the RIE while using the second resist pattern 65 as a mask, thereby forming a first trench 61 a in these insulating films 61 and 62.

The etching gas with which the etching rate of the etching stopper film 60 is lower than that of the second insulating film 61, i.e., the mixed gas of C₂F₆ gas and CH₃ gas, for example, is used in this dry etching process. In this way, the etching stops on the etching stopper film 60 and the first insulating film 42 is prevented from being etched.

Meanwhile, the first trench 61 a thus formed extends from a position over the first hole 42 a to a position over the second hole 42 b as illustrated in the second cross section.

Thereafter, the second resist pattern 65 is removed.

Next, steps to be carried out in order to obtain a cross-sectional structure illustrated in FIG. 7E will be described.

First, a tantalum film and a tantalum nitride film are formed in this order as a barrier metal film in the respective holes 42 a to 42 c as well as the first trench 61 a and on an upper surface of the antireflection insulating film 62 by the sputtering method. Although the film thickness of the barrier metal film is not particularly limited, the tantalum film is set to about 5 nm and the tantalum nitride film is set to about 10 nm in this embodiment.

Then, a copper film is formed as a seed layer on this barrier metal film by the sputtering method and a copper plated film is formed using the seed layer as a power feeding layer, thereby completely burying the respective holes 42 a to 42 c and the first trench 61 a with the copper plated film.

Thereafter, the excessive copper plated film, the seed layer, and the barrier metal film on the antireflection insulating film 62 are polished and removed by the CMP method.

In this way, first to third copper-containing plugs 70 a to 70 c are formed in the respective holes 42 a to 42 c by the dual damascene method. Moreover, in this dual damascene method, a first copper-containing interconnection 70 is formed in the first trench 61 a over the etching stopper film 60.

The first copper-containing interconnection formed by the dual damascene method is formed integrally with the first copper-containing plug 70 a and the second copper-containing plug 70 b. Meanwhile, the third copper-containing plug 70 c penetrates the first insulating film 42 and the second insulating film 61 and is electrically connected to the source-drain region 37 a.

FIG. 8B is the plan view after completion of the above-described steps. Here, the second cross section in FIG. 7E corresponds to a cross section taken along an X7-X7 line in FIG. 8B and the first cross section in FIG. 7E corresponds to a cross section taken along a Y7-Y7 line in FIG. 8B.

As illustrated in FIG. 8B, the first copper-containing plug 70 a has a rectangular planar shape so as to correspond to the first hole 42 a (see FIG. 7E).

Meanwhile, the first copper-containing interconnection 70 has an L-shaped planar shape which is formed to cover the above-described first copper-containing plug 70 a.

Even when the first copper-containing interconnection 70 is formed into the L-shape, the copper-containing pad 48 b (see FIG. 6D) is not formed on the third copper-containing plug 70 c in this embodiment unlike the first embodiment, so that it is possible to gain a space by omitting the copper-containing pad 48 b. Accordingly, it is possible to reduce the length of the memory cell C in the bit-line direction Y by curtailing the distance D between the first copper-containing interconnection 70 and the third copper-containing plug 70 c, and thereby to achieve reduction in the cell size.

Next, as illustrated in FIG. 7F, the third insulating film 52, the third copper-containing interconnection 55 c constituting the word line (WL), and the like are formed by carrying out the steps in FIGS. 5H to 5J as described in the first embodiment.

FIG. 8C is the plan view after completion of the above-described steps. Here, the second cross section in FIG. 7F corresponds to a cross section taken along an X8-X8 line in FIG. 8C and the first cross section in FIG. 7F corresponds to a cross section taken along a Y8-Y8 line in FIG. 8C.

Thereafter, as illustrated in FIG. 8D, the bit line BL and the fourth copper-containing interconnection 56 are formed over the third copper-containing interconnection 55 c by the dual damascene method as similar to the first embodiment.

In this way, a basic structure of the semiconductor device according to this embodiment is finished.

According to this embodiment, as described with reference to FIG. 7E, the third copper-containing plug 70 c is formed simultaneously with formation of the first copper-containing interconnection 70 by use of the dual damascene method.

The third copper-containing plug 70 c formed by the damascene method is formed to penetrate the second insulating film 61. Therefore, it is not necessary to provide the copper-containing pad 48 b (see FIG. 5J) for establishing contact with the third copper-containing plug 70 c and the fourth copper-containing plug 55 a (see FIG. 7F).

Accordingly, as described with reference to FIG. 8B, it is possible to arrange the first copper-containing interconnection 70 with wide margin by omitting the copper-containing pad 48 b, and to reduce the cell size by curtailing the distance D between the first copper-containing interconnection 70 and the third copper-containing plug 70 c.

Moreover, since the dual damascene method can reduce the number of steps as compared to the single damascene method, this embodiment can further simplify the process as compared to the first embodiment.

However, as illustrated in FIG. 7F, when the third copper-containing plug 70 c is formed by the dual damascene method, the depth of the third hole 42 c becomes deeper than that in the first embodiment by the thickness of the second insulating film 61. Hence an aspect ratio of the third hole 42 c is increased as compared to the first embodiment.

Such an increase in the aspect ratio may cause deterioration in burying performance of the barrier metal film, the copper plated film, and the like in the third hole 42 c. Accordingly, it may be necessary to introduce a novel film deposition apparatus or a novel process which can improve the burying performance.

To avoid this problem, it is preferable to make a diameter x₁ of the third hold 42 c as large as possible and to suppress the increase in the aspect ratio of the third hole 42 c. The same applies to a third embodiment to be described later.

The degree of the increase in the size of the diameter x₁ is not particularly limited. However, it is preferable to make the diameter x₁ larger than a diameter x₂ of the fourth hole 52 a, for example.

However, if the diameter x₁ is made too large, there is a risk of affecting reduction in the cell size. Accordingly, an upper limit of the diameter x₁ is preferably set about 1.2 times as large as the diameter x₂.

Here, when the respective holes 42 c and 52 a have tapered cross-sectional shapes as illustrated in FIG. 7F, the diameters x₁ and x₂ of these holes 42 c and 52 a at bottom surfaces of the respective plugs 70 c and 55 a are compared with each other.

By the way, in this embodiment, the etching stopper film 60 is formed between the first insulating film 42 and the second insulating film 61. The etching stopper film 60 plays a role in preventing the first insulating film 42 from being etched when the first trench 61 a is formed by etching in the step illustrated in FIG. 7D.

FIGS. 9A to 9C are cross-sectional views during manufacture of a semiconductor device according to a comparative example for explaining an advantage obtained by the prevention of etching the first insulating film 42 in this manner. In FIGS. 9A to 9C, the same constituents as those in this embodiment will be designated by the same reference numerals as those in this embodiment and description thereof will be omitted in the following.

As illustrated in FIG. 9A, this comparative example omits the etching stopper film 60 and the second insulating film 61 from this embodiment. Then, as similar to the steps described above in conjunction with FIGS. 7B and 7C, the cover insulating film 41 and the first insulating film 42 are dry etched using the first resist pattern 63 as the mask, whereby the first to third holes 42 a to 42 c are formed on these insulating films 41 and 42.

After removing the first resist pattern 63, the second resist pattern 65 is formed on the antireflection insulating film 62 similarly to this embodiment as illustrated in FIG. 9B.

Then, the first insulating film 42 is dry etched to a midway depth using the second resist pattern 65 as the mask, thereby forming the first trench 42 d in the first insulating film 42.

At this time, a bottom surface A of the first trench 42 d is not covered with the second resist pattern 65, and is therefore formed into a chamfered shape as illustrated in FIG. 9B due to exposure to an etching atmosphere.

Subsequently, after removing the second resist pattern 65, the first to third copper-containing plugs 70 a to 70 c are formed in the first to third holes 42 a to 42 c by the dual damascene method as illustrated in FIG. 9C, and the first copper-containing interconnection 70 is formed in the first trench 42 d.

According to this comparative example, since the bottom surface A of the first groove 42 d is chambered as illustrated in FIG. 9B, the distance d between the gate electrode 35 and the first copper-containing interconnection 70 becomes shorter as illustrated in FIG. 9C, thereby incurring a problem of reduction in voltage resistance between the first copper-containing interconnection 70 and the gate electrode 35.

On the other hand, in the present embodiment, since the bottom surface of the first groove 61 a is protected by the etching stopper film as illustrated in FIG. 7D, it is possible to prevent the bottom surface of the first trench 61 a from being etched and to avoid reduction in the voltage resistance between the first copper-containing interconnection 70 and the gate electrode 35.

Third Embodiment

In this embodiment, the first copper-containing interconnection 70 is formed by the dual damascene method as similar to the second embodiment. However, as will be described later, a stacked structure of the insulating films for burying the first copper-containing interconnection 70 of this embodiment is different from the second embodiment.

FIGS. 10A to 10F are cross-sectional views during manufacture of a semiconductor device according to this embodiment. In FIGS. 10A to 10F, the same constituents as those described in the first and second embodiments will be designated by the same reference numerals as those in the embodiments and description thereof will be omitted in the following.

Moreover, since the planar layout of the semiconductor device according to this embodiment is similar to that of the second embodiment. Therefore, the plan views of the semiconductor device will also be omitted herein.

To manufacture the semiconductor device according to this embodiment, the steps in the first embodiment as described in conjunction with FIGS. 5A to 5C are firstly executed, and then a second insulating film 81 is formed on the first insulating film 42 as illustrated in FIG. 10A.

The second insulating film 81 is a silicon oxycarbide film having a thickness of about 150 nm, which is formed by the CVD method, for example.

Further, a silicon oxy-nitride film serving as an antireflection insulating film 82 is formed in a thickness of about 30 nm on this second insulating film 81 by the CVD method.

Next, as illustrated in FIG. 10B, a photoresist is coated on the antireflection insulating film 82, and the first resist pattern 63 provided with the hole-shaped windows 63 a to 63 c is formed by exposing and developing the photoresist.

Then, the respective insulating films 42, 81, and 82 are sequentially dry etched by the RIE while using this first resist pattern 63 as the mask, thereby forming the first to third holes 42 a to 42 c in these insulating films 42, 81, and 82.

The mixed gas of C₂F₆ gas and CH₃ gas is the etching gas usable in this dry etching process, for example. When using this etching gas, the etching rate of the cover insulating film 41 is lower than that of the first insulating film 42. Accordingly, this etching process stops on the upper surface of the cover insulating film 41.

Subsequently, as illustrated in FIG. 10C, the cover insulating film 41 below the respective contact holes 42 a to 42 c is dry etched and removed by performing the RIE while changing the etching gas to the CF₄ gas.

Thereafter, the first resist pattern 63 is removed.

Next, as illustrated in FIG. 10D, a photoresist is coated again on the antireflection insulating film 82, and then is developed by exposure to form the second resist pattern 65 provided with the window 65 a having the wiring trench shape and overlapping with the first hole 42 a.

This second resist pattern 65 located bottom portions in the first hole 42 a and the second hole 42 b is not removed by development but is left in these holes 42 a and 42 b. Meanwhile, the third hole 42 c is completely filled with the second resist pattern 65.

Then, the antireflection insulating film 82 and the second insulating film 81 are dry etched while using the second resist pattern 65 as the mask, thereby forming a first trench 81 a exposing the first hole 42 a and the second hole 42 b at a bottom surface thereof.

The dry etching is performed by the RIE and etching gas containing either CHF-based gas or CF-based gas is used as the etching gas. Here, it is also possible to add inert gas such as argon gas or nitrogen gas to the etching gas.

When using such an etching gas, the etching rate of the first insulating film 42 becomes lower than that of the second insulating film 81. Accordingly, the first insulating film 42 functions as an etching stopper film, whereby the etching process stops on the upper surface of the first insulating film 42.

Thereafter, the second resist pattern 65 is removed.

Subsequently, as illustrated in FIG. 10E, the barrier metal film, the seed layer, and the copper plated film are formed in this order in the first to third holes 42 a to 42 c and in the first trench 81 a as similar to the second embodiment.

In this way, the first to third copper-containing plugs 70 a to 70 c are buried in the first to third holes 42 a to 42 c by the dual damascene method. Moreover, the first copper-containing interconnection 70 is formed integrally with the first and second copper-containing plugs 70 a and 70 b in the first trench 81 a.

Subsequently, as illustrated in FIG. 10F, the third insulating film 52, the third copper-containing interconnection 55 c constituting the word line (WL), and the like are formed by carrying out the steps in FIGS. 5H to 5J as described in the first embodiment.

Thereafter, the process goes to the steps of forming the insulating film on the entire upper surface of the silicon substrate 31 and then forming the copper-containing interconnection constituting the bit line BL is formed on the insulating film by the dual damascene method as similar to the first embodiment. However, the description thereof will be omitted.

In this way, a basic structure of the semiconductor device according to this embodiment is finished.

According to this embodiment, as illustrated in FIG. 10D, the first insulating film functions as the etching stopper film by using the etching gas with which the etching rate of the first insulating film 42 becomes lower than the etching rate of the second insulating film 81. For this reason, there is no risk that the bottom surface of the first trench 81 a is chamfered in this etching process. Hence it is possible to suppress reduction in the voltage resistance between the gate electrode 35 and the first copper-containing interconnection 70 as observed in the comparative example in FIG. 9C, which is attributable to reduction in the distance d therebetween.

Moreover, according to this embodiment, the first insulating film 42 is used as the etching stopper as described above. Therefore, it is not necessary to provide the etching stopper film 60 formed in the second embodiment. Hence the process can be further simplified as compared to the second embodiment.

All examples and conditional language recited herein are intended for pedagogical purposes to aid the reader in understanding the invention and the concepts contributed by the inventor to furthering the art, and are to be construed as being without limitation to such specifically recited examples and conditions, nor does the organization of such examples in the specification relate to a showing of the superiority and inferiority of the invention. Although the embodiments of the present inventions have been described in detail, it should be understood that the various changes, substitutions, and alterations could be made hereto without departing from the spirit and scope of the invention. 

1. A semiconductor device comprising: a semiconductor substrate in which a first active region and a second active region of a memory cell of a static random access memory are defined by a device isolation insulating film; a gate electrode formed over the device isolation insulating film and the first active region, and extending in a first direction; a first insulating film formed over the semiconductor substrate and the gate electrode; a first plug formed to penetrate the first insulating film, to overlap with the gate electrode and the first active region, and to have a rectangular planar shape extending in a second direction perpendicular to the first direction; a second plug formed to penetrate the first insulating film over the second active region; a second insulating film formed over the first insulating film; and a interconnection buried in the second insulating film, and formed to extend from a position over the first c plug to a position over the second plug while receding from a side surface of the plug in the second direction, and to cover only a part of an upper surface of the first plug.
 2. The semiconductor device according to claim 1, further comprising: a third plug formed to penetrate the first insulating film; a pad buried in the second insulating film over the third plug and around the third plug; a third insulating film formed over the second insulating film; and a fourth plug formed to penetrate the third insulating film over the pad.
 3. The semiconductor device according to claim 2, wherein; the first plug, the second plug, the third plug, and the fourth plug include copper.
 4. A semiconductor device comprising: a semiconductor substrate in which a first active region and a second active region are defined by a device isolation insulating film; a gate electrode formed over the device isolation insulating film and the first active region and extending in a first direction; a first insulating film formed over the semiconductor substrate and the gate electrode; a first plug formed to penetrate the first insulating film, to overlap with the gate electrode and the first active region, and to have a rectangular planar shape extending in a second direction perpendicular to the first direction; a second insulating film formed over the first insulating film; a second plug formed to penetrate the first insulating film and the second insulating film over the second active region; a interconnection formed in the second insulating film, formed integrally with the first plug and the second plug, and extending from a position over the first plug to a position over the second copper-containing plug; and a third plug formed to penetrate the first insulating film and the second insulating film.
 5. The semiconductor device according to claim 4, further comprising: a third insulating film formed over the second insulating film; and a fourth plug formed to penetrate the third insulating film over the third plug, wherein a diameter of the third plug is larger than a diameter of the fourth plug.
 6. The semiconductor device according to claim 5, wherein the diameter of the third plug is a diameter at a bottom surface of the third copper-containing plug, and the diameter of the fourth plug is a diameter at a bottom surface of the fourth copper-containing plug.
 7. The semiconductor device according to claim 4, wherein an etching stopper film is formed between the first insulating film and the second insulating film, and the interconnection is formed over the etching stopper film.
 8. The semiconductor device according to claim 5, wherein; the first plug, the second plug, the third plug, and the fourth plug include copper.
 9. The semiconductor device according to claim 4, wherein the first insulating film is an etching stopper film for the second insulating film.
 10. The semiconductor device according to claim 1, wherein the first active region comprises a source-drain region of a load transistor included in the memory cell, and the second active region comprises a source-drain region shared by a driver transistor and an access transistor included in the memory cell.
 11. A method of manufacturing a semiconductor device comprising: defining, in a semiconductor substrate, a first active region and a second active region of a memory cell of a static random access memory by forming a device isolation insulating film over the semiconductor substrate; forming a gate electrode, extending in a first direction, over the device isolation insulating film and the first active region; forming a first insulating film over the semiconductor substrate and the gate electrode; forming a first hole in the first insulating film, the first hole overlapping with the gate electrode and the first active region and having a rectangular planar shape extending in a second direction perpendicular to the first direction; forming a second hole in the first insulating film over the second active region; forming a first plug and a second plug respectively in the first hole and the second hole; forming a second insulating film over the first plug, the second plug, and the first insulating film; forming a trench in the second insulating film, the trench extending from a position over the first plug to a position over the second plug, the trench being formed at a distance from a side surface of the first plug in the second direction; and forming a interconnection in the trench.
 12. The semiconductor device according to claim 11, wherein; the first plug and the second plug include copper.
 13. A method of manufacturing a semiconductor device comprising: defining, in a semiconductor substrate, a first active region and a second active region of a memory cell of a static random access memory by forming a device isolation insulating film over the semiconductor substrate; forming a gate electrode, extending in a first direction, over the device isolation insulating film and the first active region; forming a first insulating film over the semiconductor substrate and the gate electrode; forming a second insulating film over the first insulating film; forming a first hole, a second hole and a third hole by patterning the first insulating film and the second insulating film, the first hole having a rectangular planar shape overlapping with the gate electrode and the first active region and extending in a second direction perpendicular to the first direction, the second hole being located over the second active region; forming a trench by patterning the second insulating film, the trench extending from a position over the first hole to a position over the second hole; and forming first, second, and third plugs in the first, second, and third holes and forming an interconnection in the trench, thereby forming the interconnection integrally formed with the first plug and the second plug.
 14. The semiconductor device according to claim 11, wherein; the first plug and the second plug include copper. 